Continuous tunnel kiln and method of operating the same



Jan. 22, 1935. P. DH. DREssLER 1,983,337

CONTINUOUS TUNNEL KILN AND. METHOD OF OPERATING THE SAME Filed Sept. 4, 1951 5 Sheets-Sheet 1 :IIWIHIIIHIWINWIHIIIHWII I NHIIIIHIHIUIWIIIIIIIIIIIHIWWHIIIIIIIHMW WIIIIMWWWMWIHIMIIIMWIHIIIHHIWI. I I I V I I I I @mvv v\ MGIWVIN@ TM. Mw w@ @www Jan. 22, 1935. P. D'H. DREssLER 1,988,837

CONTINUOUS TUNNEL KILN AND METHOD OF OPERATING THE SAME Filed Sept. 4, 1931 5 Sheets-Sheet 2 Jm. 22, 1935. P. DH. DRl-:ssLER 1,988,837

CONTINUOUS TUNNEL KILN AND METHOD OF OPERATING' THE SAME Filed Sept. 4, 1931 5 Sheets-Sheet 5 N V EN TOR.

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Patented Jan. 22, 1935 lUNITED `STATES CONTINUOUS TUNNEL KILN AND METHOD oF OPERATING THE SAME.k

Philip dHuc Dressler, Pittsburgh, Pa., assigner Y to Swindell Dressler Corporation, Pittsburgh, 'l

Y Pa., acorporation of Pennsylvania* Application September 4, 1931, Serial No. 5161,119 I claims. (ol. 263-28) My present invention relates to continuous tunnel kilns, and particularly to open re kilns in which the gaseous products of combustion of the fuel used in heating the kiln pass into the goods 5 space of the kiln from combustion chambers in which the combustion of the fuel is initiated and Wholly or largely completed.

My present invention consists in improvements in kiln structure and arrangement, and in meth-y ods of kiln operation, devised With the, general ob`` ject in View of securing a desirable heat distribu-l tion in the kiln goods space, and particularly in the main heating section of said space, and of modifying said distribution as co-nditions make desirable, with a kiln structure and heating means which are desirably simple, effective, relatively inexpensive and durable, and Which permit of a rapid rate of supply of heat to the heating portion of the kiln, and hence of high capacity kiln operation Without subjecting the goods or goods containers to the direct impingement of 'high temperature heating gases moving at high velocity, or otherwise subjecting thev goods or the kiln structure to injurious local overheating.

In accordance with the present invention, I emp-loy combustion chambers which are distributed along the sides of the heating zoneof the kiln as has been customary, but which differ from those heretofore employed in that they are arranged to pass heatinggasesV into the goods space adjacent both the top and bottom of the latter, but which do not pass heating gases directly into contact with the sides of the masses or stacks of goods moving through the goo-ds space of the kiln. In the preferred embodiments of the present invention the heating gases pass intothe kiln goods space from the combustion chambers through combustion chamber Wall ports distributed along the lengths of the combustion chambers in upper and lower sets.

In accordance With the present invention, the heating gas discharge rates through the different ports are proportioned to insure proper relative amounts of heating Vgas flow into the top and bottom portions of the goods space, andalso-into the different longitudinal portions of the goods-space of the kiln. Such proportioning may Well vbe secured, and varied as conditions make desirable, in part by the dimensions initially given the ports, and in part by the use of adjustable throttling dampers or obturators associated with some or all of the ports. In practice, I have found that in some kilns at least, the desireddistribution can be secured by means of adjustable throttling dampers associated with one set only of the above mentioned upperY and lower sets'of combustion chamber outlet ports. With only the outlet ports of one set provided with dampers, it .is readily possible, of course, to vary the relative amountsof heating gases discharged throughthe upper and lower sets of ports, and I. have also foundthat by the adjustmentof the dampers of one set only, .and by the lregulation of the'fuel `supply to the different combustion chambers, :an Y

adequate Variation of the total inflow of heating gas into different longitudinal portions of the goods spacemay be securedz! .1'

Heretofore it has been proposed todischarge heating gases into the goods space of open vfire kilns 'either Wholly at the bottom.' or wholly at the top of the goods space,:andl it hassalso been. proposed to discharge theheatinggases into' the goods space through ports distributed, both hor-,- izontally and vertically, along the sides of :said space. `I haveA found, however, thatnone of the methods of introducing'the heatingfgase's Yjust mentioned, will give satisfactory kiln heating at least formany of :the 4purposes for which said kilns are used. ,When all the :heating gases are introduced into the goods space -atthe bottom of the latter, there is ordinarily laY pronolmced and objectionable tendency to overheat the goods 'in Ythe lower portion ofthe goods' space. When all the'heating gases are introduced into`the goods space adjacent the top ofy the latter,rv .local overheating of the goods in the upper portion ofthe goods space is inevitable. When any I'considerable portion of the heating gases' Adirectlyenter the goods space at the sides of the'lattenflocal overheating of the goods at the sides of the goods space is inevitable.

Local overheating of rthe goods in any portion of the goods space is always objectionable. With many classes of goods, it results in the production of ya considerable amount of imperfect second grade or useless goods. v'Local overheating 'of' the goods at the sides ofth'evgoods space is particularly objectionable in the case of coarse clay products `suclia's paving brick, which even though not directly injured by the 'overheating are thereby` subjected to unequal shrinkage which not only prevents uniformity in nished brick dilmensions and shapes, but tends todisplace the bricksv stacked on thev cars. 'Such displacement may and occasionally does result in injury to the kiln structure and cars which delay and add to the expense ofy kiln operation.

"Under ordinary practical'conditions ofy kiln operation, the relative heating requirements of different portions ofthe goods space vary from time to time as a result of changes in the character of the goods fired, changes in the rate at which goods are moved through the kiln, and of other causes, and my present invention is therefore of especial value because it makes possible easy and accurate Variations in the distribution of the heating gases passing to different portions of the goods space as conditions may require.

In accordance with the present invention, I

also make use in some cases of provisions for effecting a local recirculation of the kiln atmosphere by drawing gas fromthe Vgoods space into the combustion chamber, mixing it with the products of combustion formed therein and discharging the mixture into the goods space through the combustion chamber outlets. This procedure, in addition to effecting a local longitudinal circulation of the goods space atmosphere, highly desirable of itself in some cases, effects a reduction in the maximum combustion chamber temperature, thereby reducing the liability rto local overheating of the kiln structure and local overheatving of the goods, the latter being of especial importance in metal annealing and other kilns in which the maximum goods space temperature is relatively low.

The general features of the present invention may be used with advantage in kilns employed for a wide variety of purposes and requiring very 'different goods space temperature conditions, and without regard to the character of the fuel used, which may be a rich gas such as natural gas, a lean gas such as producer gas, oil, or coal, as conditions make desirable.

The' various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its characteristics, advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter, in which I have illustrated and described preferred embodiments ofthe present invention.

0f the drawings:

Fig. 1 is a somewhat diagrammatic plan view of a tunnel kiln;

Fig. 2 is a' partial section'on'the line 2 2 of Fig. 1, with an inner combustion chamber wall portion broken away to 4show the kiln car structure; Fig. 3 is a transverse sectionon the broken line 3-3of Fig. 1;

i Fig. 3A is a transverse Vsection on the line 3A-3A of Fig. 2;

Fig. 4 is a view, generally similar'to Fig. 1, of a kiln differing in type from that shown in Fig. 1;

Fig. 5 is a section on the broken line V5---5 of Fig. 4; and

Fig. 6 isa partial horizontal section on the line 6-6 of Fig. 5. 1

In Figs. 1, 2, 3 and 3A of the drawings, I have illustrated an embodiment of the present invention in a continuous tunnel kiln A especially devised and adapted for use in annealing malleable 'castings In the kiln shown in Figs. 1, 2, 3 and 3A, the whole or main heating effect is obtained lby the combustion of fluid fuel in combustion chambers B, distributed along a substantial portion of the length of the kiln at each side of the latter. In Fig. 1, A' represents a heating gas outlet connection leading to a chimney or exhaust fan (not shown) which withdraws from the kiln the Waste heating gases entering the kiln goods space from said combustion chambers B. The

kiln heating effect of the combustion chambers B may, or may not, be supplemented by the heating effect of burners supplying heating gases to the cooling zone section of the kiln, as conditions of operation make desirable. I have not though it necessary to illustrate such supplemental burners, as their construction and arrangement constitute no part of the present invention and may be in accordance with known prior practice.

In the kiln shown in Figs. 1-3, the combustion chambers B are arranged in end to end pairs in Aside bays or lateral enlargements A2 of the kiln chamber, and the burners for the two combustion chambers in each bay are located in, or extend into the opposite end walls of the bay, the adjacent endvto end bays being spaced far enough apart to permit ready access to the burners through the space between the adjacent bay ends and at the outer side of the narrower portion of the kiln connecting the bay enlargements of the latter.

The combustion chambers B may well take the form of suitably shaped cavities in the main side walls of the kiln structure, but as shown in Figs. 1 to 3A, each combustion chamber comprises inner and outer side walls b and b2, a bottom wall b3, a top wall b4 and end walls b5, all separate from the main kiln wall and supported on a bench or bottom wall portion A4 of the corresponding bay. The formation of the combustion chamber walls separate from the main kiln walls, has the advantage of confining the injurious effects of local combustion chamber overheating to the walls of the combustion chamber, thereby facilitating, and

reducing the cost of repairs which may occasionally become necessary as a result of such overheating.

The end wall b5 of each combustion chamber adjacent the end of the bay containing said chamber, is formed with an inlet bf through which fluid fuel and air for its combustion enter the combustion chamber. In accordance with the present invention the heating gases pass from each combustion chamber into the kiln chamber proper through a set of bottom outlet ports C, and a set of upper outlet ports D suitably distributed along the length of the combustion chamber. As shown the main portion of the inner side wall b of each combustion chamber is spaced away from the adjacent side of the goods space proper, but is provided with a lateral enlargement b1 at its lower end, in which the outer end portions of the ports C are formed. Those ports extend into close proximity with the outer ends of, and may advantageously be proportioned and arranged to permit them to register with, the usual horizontal heating gas channels E formed immediately beneath the goods supporting platforms E2 of kiln cars E which run on the kiln track rails a, and collectively form a movable hearth for transporting goods through the kiln.

The upper combustion chamber outlet ports D are shown as extending vertically through each combustion chamber top wall b4. The latter is separated from the portion of the kiln crown or roof A5 directly above it, by a space through whichv the heating gases issuing through the ports D pass into the goods space. Conveniently, the top walls b4 of the combustion chambers B may be at a level approximately midway between those of the top and bottom of the goods space. A barrier wall 1211, which may be in the form of an upward extension of the inner wall b of each combustion chamber, extends upward from the combustion chamber top Wall b4 far enough to deflect Losses? the heatin'g gas streams issuing through the ports -D into the goods space adjacent the top of `the latter. In consequence the heating gases issuing through the ports D do not directly `impinge against the goods at the sides of the goods space, l

but come into contact with the goods only after their initial velocity has been largely dissipated, and4 their Atemperature has been reduced by admixture with Athe main body of gas in the space directly above the combustion chamber.

As previously explained it is ordinarily desirable to regulate the amount of heating gas discharged through the bottom outlet ports of each combustion chamber relative to the amount discharged through the vupper outlet ports by means of dampers or obturators associated with all or some of said outlet ports. `In the construction shown in Figs. 1 to 3A, the bottomoutlet ports C are not provided with regulating dampers or obturators, but each upper outlet port D is provided with a damper F shown as of the slide bricktype. Each damper F maybe adjusted as required through a suitably normally closed damper adjustment opening Arl formed in the lateral Wall of the kiln structure.

In the kiln illustrated in Figs. 1 to 3A oil and air for the combustion of the oil are passed into each combustion chamber B through the burner opening b6 in one of its end walls b5 by an oil burner G mounted in the corresponding bay end Wall. The jet discharge of each burner G enters the interior of the kiln through a nozzle opening A10 in the corresponding bay end wall. As shown the nozzle opening A10 is in axial lalignment with the corresponding combustion chamber inlet opening be, and the walls in which those openings are formed are spaced apart, thus providing a small chamber H between those walls. Between each chamber H and the goods space of the kiln is a Wall D which may be formed by an end extension or" the inner wall b of the corresponding combustion chamber. Each chamber H communicates with the goods space of the kiln through `a bottom port H in the wall Z215, and may communicate with said space through a port H2 at its upper end. Advantageously and as shown, the extent of such communication through the upper end of each chamber may be controlled by the adjustment of a corresponding damper h which is adjustable through an adjustment opening A11 formed in the corresponding bay end wall.

With the arrangement illustrated in Figs. l, 2 and 3, the fuel and air jet discharge from each burner G passes across the corresponding chamber H at the outlet end of the nozzle opening A10 into the combustion chamber opening be, and by its aspirating action draws gas through the chamber H and into the combustion chamber B from the goods space of the kiln. The amount of gas thus drawn into each combustion chamber B through the associated chamber H may be regulated by adjustment of the corresponding damper h. The recirculation gas iiow from the goods space of the kiln through the chambers H into the combustion chambers B and thence back into the goods space through the ports C and D, creates a local longitudinal circulation of the kiln atmosphere which assists materially in obtaining the desired heat distribution in some cases and which always reduces both the maximum :and the average combustion chamber temperatures. Such temperature reduction reduces the risk of local overheating of the kiln structure, and by reducing the temperature of the gas jets dis- .charged through the ports C and D, reduces the tendency. to local .overheatingA of the'goods, a matterA of especial importance in akiln such as a metaln annealing. kiln in which. the maximum goodsy temperature is'relatively low.

Where the. local kiln temperature circulation and combustion chamber reducing actions of the 'chambers H are not required', the chambers H Vmay nevertheless be employed with advantage in .some cases, in effecting the introduction of highly Such connections need not be illustrated and de- :scribed herein, as they may be exactly similar to those disclosed-in my said prior patentkfor supplying hot air tothe aspiratingy burners of said patent.

In the particular arrangement shown in Figs. l to 3A, malleable castings 'to' be annealed or other goods to be heated are held in pots e stacked on the Work-supportingplatforms E2 of the goods cars E. The bricks or tiles. E3 forming the portion of the refractory car superstructure of each car E immediately below its Work supporting platform E2 are varranged to form the'side and bottom walls of the heating-gas channels ET. The latter extend from one side `to the other of the car and are open at their ends. Refractory slabs E2 form the goods supporting platform ot` the car, and also cover the major portions of its channels E.

Through the uncovered portions of the channels E the heating gases entering the latter from the ports C maypassupward into thegoods space of the kiln at the sides lof the potse. The usual sand seal'provisio-ns E4 prevent gas flow between the goods space proper, and the space beneath the hearth formedby the carl bodies. Suitable sandfsea-l yinspection openings A6 are formed in the sidel Wallsoffthe kiln structure.

The general operation of `the kiln shown in Figs. 1 to 3A will be readily apparent to those skilled ingthe art. As the goods 0n any particular kiln car E move progressively through the kiln preheating section A20, through the main heating section` in which the combustion chambers B are located, and through the cooling zoneA30 of the kiln, the temperature of-the goods is raised more or less gradually to its maximum value, and is subsequently reduced more or less in accordance with the heat cycle or Atreatment to whichsth goods areto be subjected. y

The amountoflieatsupplied by each combustion chamber B can be increased or decreased by adjustment of theA corresponding burner G. The distribution of heat tothe goods space from each combustion chamberrmay be varied as conditions require, both longitudinally of the kiln and in a vertical, direction, by suitable manipulation of the dempers F associated with the upper outlet ports D. The heat distribution is also subject to regulationby adjustment of the diiierent dampers h. The adjustment of the dampers h varies the local longitudinal flow of the goods space atmosphere produced by the aspirating eifecty of the burners G on the gas enteringthe chambers H, and also varies the heat distribution in the goods space somewhat by varying the relative iniiows into the chambers H `through the upper vends of the latter and through the ports H.

By the conjoint use of the various heat distribution controlling devices theA temperature conditions in different portions of the main heating zone section of the goods space can be closely regulated as conditions of operationv make necessary or desirable. The actual temperatureconditions existing are determinable in the usual way, of course, by means of suitably disposed pyrometers I. As has been previously explained in detail, the recirculation producedi by the aspirating action of the burners G on the gas in the chambers H reduces the combustion chamber temperatures and minimizes the liability to local overheating of the combustion chambers and the goods.

While the particular kiln structure shown. in Figs. 1 to 3A was especially designed, for use in metal vannealing operations in 'which the. maximum goods space temperature is relatively low, the general features of the presentinvention are not restricted to use in annealing kilns, or in kilns in which the maximum goods space temperature is relatively low, or in kilns heated by the combustion of fluid fuel, and in Figs. 4, 5 and 6 I have illustrated by way of example the use of general features of the present invention in a kiln AA suitable for use in firingy paving brick, and in which the maximum kiln temperature is much higher than in an annealing kiln, and in which the sole or main heating action results from the combustion of coal burned on grates.

'Ihe kiln AA is in many respects like the kiln A, and some of the parts of the two kilns which do not differ significantly from one another are designated by the same reference letters. The main heating zone portion of the kiln AA is of uniform width, but to accommodate the combustion chambers BB mounted thereinis made Wider than the kiln preheating and cooling zone section A20 and A30 respectively. The latter may be generally similar in form to the combustion chambers B of Figs. 1, 2 and 3, and, as' shown, comprise inner and outer Walls bb', hb2, `a top wall bb4 and end walls bb5, generally similar to the walls b', b2, b4 and b5, respectivelyfofithcombustion chambers B.y The walls bb and bib1 are formed with ports C and D, respectively, and the wall bb is extended upwardly to form a barrier Z211 like that shown in Figs. 1 to 3A. With the construction shown in Figs. 4, 5 and 6, however', the combustion chambers BB do not receive uid fuel through burner ports in their end walls. On the contrary, each combustion chamber BB is shown as receiving burning gases at a point midway between its ends through a port D20 in its outer wall hb2, from the fire box K of a corresponding furnace chamber K which projects laterally outward from the lower portion of the side Wall ofthe kiln structure. f Y

As shown, each furnace K is provided with a grate K20 between its fire box K and subjacent ashpit K2. The fuel bed on each furnace grate may be trimmed and replenished by hand firing through a doorway K3 in the outer Wall of the furnace. Ordinarily, however, coal is fed to each fire box by a suitable stoker L associated with the corresponding furnace. The nre box K' of each furnace K and the associated combustion chamber BB are in direct communication through the corresponding port b2", and each combustion chamber BB is in effect an extension of the cornbustion chamber or fire box of the corresponding furnace K. Air for combustion is supplied to the ashpit K2 of each furnace through an inlet K4 which may be connected to the outlet of a blower.

The wall bb of each combustion chamber B is shown as differing significantly from the corresponding wall b of Figs. 1 to 3A, only in having a thickened imperforate central portion bbll which is in line with the port b2 and is formed with oppositely inclined surfaces facing said port. This thickened portion bb11 of the Wall bb provides a suitable name impact surface and deflects the burning and unburnt gases entering the combustion chamber BB toward the opposite ends of the latter. As no ports C are formed in the wall portion bbll, the latter prevents the gases from entering the kiln goods space incompletely burned and at high velocity as they may enter the combustion chamber BB through the port D20 from the fire box K.

By the discharge of the heating gases in the goods space of the kiln in suitably proportioned amounts through the lower and upper sets of ports C and D provided in each of the kilns, the same general advantages are obtained with the kiln AA of Figs. 4, 5 and 6, as with the kiln shown in Figs. 1 to 3A.

While in accordance with the provisions of the statutes, I have illustrated and described the best formsV of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the forms of the apparatus and methods disclosed without departing from the spirit of my invention as set forth in the appended claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention what I claim as new and desire to secure by Letters Patent, is:

1. The improved method of operating an open fire continuous timnel kiln comprising a plurality of combustion chambers distributed along the length of the kiln goods space each of which discharges heating gases into said space, which consists in mixing products of combustion formed in each combustion chamber with gas passed into the latter from the adjacent portion of the goods space, in such manner that the temperature of the heating gases passing from each combustion chamber into the goods space is reduced and a local longitudinal circulation of the goods space atmosphere is effected, and varying the amounts of gas so passed into the different combustion chambers to thereby vary the heat distribution in the goods space.

2. The combination in an open flre continuous tunnel kiln of combustion chambers at the sides of the kiln goods space each of which discharges heating gases into said space, burner means discharging uid fuel jets into the combustion chambers, and means associated with said burner means for passing gas from the goods space of the kiln into contact with said jets whereby the aspirating action of the latter moves said gas into the combustion chambers.

3. The combination in an open fire continuous tunnel kiln of a combustion chamber at the sides of the kiln goods space and discharging heating gases into said space having a burner inlet which is in communication at its outer end with the kiln goods space, and means for discharging a fluid fuel jet into said chamber through said inlet and thereby returning gas from the goods space into the combustion chamber by the aspirating action of -said jet.

4. The combination in a continuous tunnel kiln comprising alternate narrow and wide portions, of combustion chambers located in said wide portions, and a fluid fuel burner for each combustion chamber located in a transverse Wall of the corresponding Wide portion of the kiln, the adjacent end Wall of the combustion chamber being formed with a burner inlet opening through which said burner discharges a fuel jet into the chamber and being separated from said transverse Wall by a space communicating With the goods space of the kiln and across Which said fluid fuel burner draws gas from the goods space into the combustion chamber by its aspirating action.

5. The combination in a continuous tunnel kiln comprising alternate narrow and Wide portions,

of combustion chambers located in said wide portions, and a fluid fuel burner for each combustion chamber located in a transverse Wall of the cor-V responding Wide portion of the kiln, the adjacent end wall of the combustion chamber being formed with a burner inlet opening through which said burner discharges a fuel jet into the chamber and being separated from said transverse Wall by a space communicating with the goods space of the kiln and across which said fluid fuel burner draws gas from the goods space into the combustio chamber by its aspirating action. f

PHILIP DHUC DRESSLER. 

